I think you need to purchase a USB-UIRT and then learn some commands to control your devices.
For instance, in my living-room, I have the LMCE MD, a LCD TV and a stereo. With the USB-UIRT connected to the MD, I was able to "teach it" some commands, like power on/off, volume up/down, mute, etc.
So now, to answer your questions, we just click the big green media button on the gyro remote and presto! LMCE turns on the TV and the Stereo for us.
To power down, I go to Advanced > Power > MD Display Off and LMCE turns off the TV and Stereo.
I love this part of the system. It will even turn off the Tv and Stereo when I walk away from it (as long as no media is playing).
On our Windows MCE Remote, we can press the little TV button and it will turn on the TV but not the Stereo (or maybe the other way around) but on that remote if we press the green Media button in the middle, everything comes on as it should.
Also with everything programmed in, when the Tv and Stereo are off, we can open up the dvd drive tray, insert a DVD, close the dvd drive tray and go sit on the couch and LMCE will turn on the TV and Stereo for us.
The wiki has info on the USB-UIRT and other options that do the same.
This might get you started:http://wiki.linuxmce.org/index.php/USB_UIRThttp://wiki.linuxmce.org/index.php/Add_support_for_new_remote_controlshttp://wiki.linuxmce.org/index.php/Control_LinuxMCE_using_an_Infrared_remote